Useless. The drivers are horrible and the state of the tooling is insanely bad. The vendors have no clue, Intel personnel have no clue as they don't care about OpenCL 2.0 but will still gladly charge $10,000 in licenses if you really want to go that route. Verilog/VHDL is wtf, and you still need to redo your drivers.
So much potential.
I talked to a couple companies that use these in production, they reveal that they wrote their own drivers and still have issues.
You pretty much have to be a Microsoft doing sci-fi tech to get the benefits out of these, and it doesn't have to be that way.